For removing and mounting tires from and onto their respective wheel rims it is known to use suitable the removal machines which will not be described in detail herein.
To remove the tire the tire beads have to be previously separated from the respective bead-holding edges of the wheel rim.
Modern tire removal machines are provided with a bead release device for effecting this separation.
Bead release devices are known comprising an arm positioned to the side of the base of the respective tire removal machine and hinged to said base on a rear vertical axis.
Said arm is provided at its front with a bead release tool, commonly known as a blade, with which there is associated a locator positioned to the side of said base and arranged to act as a support for the wheel rim during the tire bead release.
Finally, between said arm and base there is a pneumatic cylinder-piston unit which is coupled to the arm with unilateral engagement.
Specifically, said coupling is achieved by a vertical pin which is rotatably mounted on said arm and is provided with a diametrical hole into which the rod of said cylinder-piston unit is slidingly inserted, said rod being provided with a terminal head for drawing said arm towards said locator.
The procedure for effecting bead release with said known devices is as follows.
At the commencement of a bead release operation the rod of the cylinder-piston unit is completely extended and the arm has rotated into its rest position, in which it is spaced apart from said locator.
The wheel (rim plus tire) is then placed upright resting against said locator, and the arm is made to approach the locator, with the bead release tool brought into contact with the tire bead a short distance from the bead-holding edge of the wheel rim.
During this approach the cylinder-piston unit remains in the preceding configuration, with the arm sliding along the (extended) rod of the cylinder-piston unit, so withdrawing from the terminal head of the rod.
After this approach the cylinder-piston unit is made to contract, its rod then dragging the arm and hence the bead release tool towards the wheel only after the rod head has made up the distance which separates it from the hinge pin between the rod and arm.
Basically, the actual bead release action begins only after the rod has undergone a certain idle travel, this idle travel resulting in the following drawbacks.
Firstly, said idle travel results in relatively long bead release times, which increase as the width of the wheel to undergo bead release increases.
Secondly, this idle travel results in wastage of compressed air. It will be apparent that such problems increase considerably if in order to separate a tire bead the bead release tool has to be positioned in different circumferential regions of the bead, this being necessary if the bead is tightly attached to the respective bead-holding edge and/or to the corresponding ridge.